But the implications of their decision could stretch far beyond the county's boundaries, although just how far remains a matter of debate. MARTA is pinning hopes of enlarging its territory and acquiring state funding on the outcome.

MARTA Board Chairman Robbie Ashe believes that a vote indicating strong support for expansion in Clayton will show recalcitrant metro Atlanta counties such as Cobb and Gwinnett the value of joining MARTA. Cobb and Gwinnett officials, however, expressed doubt that Clayton's vote would reverberate into their localities.

Voter approval of a 1-percent sales tax to fund MARTA could also help make a case to state lawmakers -- a committee of whom are currently exploring how to solve the state's $74 billion transportation funding gap -- that the transit agency is a worthwhile investment, said Ashe. MARTA is the only public transit agency of its size in the nation that does not receive any dedicated state funding.

The county's tax rate would go from 7 to 8 percent if the referendum passes. The proceeds would amount to $40 million to $50 million a year -- enough to pay for local bus service and either a heavy rail expansion or a bus rapid transit line.

Not everyone in Clayton is in favor of a MARTA expansion. Opponents include those against tax hikes and those who fear transit will bring more crime to the county.

But if Clayton does roll out the welcome mat, it would signal to lawmakers that many metro Atlantans not only want more transit, but they are willing to open their wallets for it, Ashe said.

"A strong Clayton result in favor of MARTA probably goes a long way towards reassuring politicians in the General Assembly and other jurisdictions that if people are given the choice to vote on MARTA, people will," Ashe said.

When the General Assembly first approved MARTA as the comprehensive transportation system for the city in 1965, it was envisioned as operating in all five of the core metro counties: Cobb, Gwinnett, Clayton, DeKalb and Fulton. However, the suburban counties of Cobb, Gwinnett and Clayton have repeatedly rejected MARTA when given an opportunity to join the system by paying a penny sales tax.

County leaders in Cobb and Gwinnett say their constituents aren't likely to be greatly influenced by what happens in Clayton even now.

Cobb County Commission Chairman Tim Lee, who has long advocated building a bus rapid transit system in Cobb, said he is personally curious about whether voters in Clayton will approve a separate funding mechanism to pay for transit. But he doubts the referendum will influence Cobb voters' attitudes about MARTA.

"We are two different geographical areas with different characteristics," said Lee. "We already have MARTA buses going to Cobb as part of our transportation system. And we have a robust system. So they are trying to catch up a little bit with where we are."

Gwinnett County Commission Chairman Charlotte Nash was even more noncommittal about the potential impact of the Clayton referendum. She said county leaders will be following all the political and referendum issues across the region.

"We have a general interest in the Clayton referendum, but not a heightened one beyond the norm," Nash said.

Chuck Warbington, chairman of the Gwinnett Village Community Improvement District, said he did not view the Clayton vote as a litmus test for MARTA's acceptance in Gwinnett. He believes a transit line is critical to the future success of the county. But in his opinion, who would operate it isn't as important as deciding where it would go and what areas it would connect.

The trend toward embracing transit has already started in much of the metro area, said Tad Leithead, who chairs the Cumberland Community Improvement District. It will be up to MARTA to capitalize upon that pendulum shift by proving it has the ability to competently manage a larger system if given the chance.

The transit agency has already begun to turn around its image from a cash-strapped and perpetually dysfunctional operation to one with its financial house in order. Over the past two years, MARTA has expanded bus and rail service while at the same time implementing extensive cost-cutting measures that put the agency back in the black.

Tuesday's vote will be the first opportunity for the public to make a statement about how far it believes MARTA has come.

A decision by Clayton County to participate in MARTA could be a "watershed event for MARTA's acceptance across the board," Leithead said. Whether that acceptance will ever translate into state dollars remains to be seen.

State Rep. Jay Roberts, R-Ocilla, said the General Assembly is well aware of the turnaround that MARTA General Manager and CEO Keith Parker has engineered since he took the job about two years ago. They are impressed, he said.

But the state's funding hole is a gaping one. And so far, the legislative study committee that is weighing transportation funding solutions has been focused on finding money for improving roads and bridges.

"At this point we don't have a final plan in place," said Roberts, who co-chairs the committee. "I do think from my standpoint, nothing is off the table."

Federal regulations neither require schools to test their water nor have a single health standard for drinking water. The resulting patchwork of state policies can have a big impact on how -- and whether -- they respond to lead found in water.